Engines may include a manifold pressure sensor positioned in an intake manifold of the engine for determining manifold pressure (MAP). An engine controller may use the measured MAP to adjust engine operation and/or determine additional engine operating parameters. For example, engine torque and or air charge inducted into engine cylinders may be at least partially based on MAP. If the MAP sensor becomes degraded or has an offset causing the MAP sensor output to be different than the actual MAP, engine adjustments based on the MAP sensor output may have reduced accuracy.
Other attempts to address MAP sensor degradation or offset include comparing outputs of additional engine pressure sensors to MAP sensor readings. One example approach is shown by Yu et al. in U.S. Pat. No. 7,171,301. Therein, a plurality of samples obtained from a MAP sensor is compared to a plurality of samples from a mass air flow (MAF) sensor. An offset of the MAP sensor is determined based on this comparison.
However, the inventors herein have recognized potential issues with such systems. As one example, in some engine, the MAP sensor may be the only available pressure sensor. Thus, comparing MAP sensor readings to a MAF sensor or any other pressure sensor may not be possible.
In one example, the issues described above may be addressed by a method for indicating degradation of a manifold pressure sensor based on a sensor offset, the sensor offset based on a manifold pressure measured at a first throttle angle, a barometric pressure at a second throttle angle, a reference manifold pressure at the first throttle angle and reference barometric pressure, and the reference barometric pressure. For example, a ratio of the barometric pressure (BP) at the second throttle angle and current altitude to the BP at a reference altitude (e.g., the reference BP) may be substantially the same as a ratio of manifold pressure (MAP) at the current altitude and first throttle angle (e.g., current MAP) to a MAP value calculated at the reference altitude (e.g., reference MAP). The reference BP may be based on a pre-determined BP at a reference altitude (e.g., BP at sea level). The BP at the second throttle angle may be based on an output of the manifold pressure sensor during one of engine operation at wide-open-throttle or engine key-on. Additionally, the reference MAP may be determined based on one or more of the current (e.g., first) throttle angle, the reference BP, engine speed, mass air flow, and/or cam position. As such, the reference MAP may be determined at the reference BP and first throttle angle. In one example, the first throttle angle may be smaller than the second throttle angle.
Indicating degradation of the MAP sensor may include indicating degradation when the sensor offset is greater than an offset threshold. Further, an output of the MAP sensor may be adjusted by the determined sensor offset. Subsequently, an engine controller may adjust engine operation based on the adjusted MAP sensor output. As a result, MAP values determined at the MAP sensor and adjusted by the sensor offset may be more accurate than unadjusted MAP outputs. This may result in more accurate engine control.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.